key: cord-0720003-imm9ima9
authors: Soriano, Vicente; Ganado-Pinilla, Pilar; Sanchez-Santos, Miguel; Gómez-Gallego, Felix; Barreiro, Pablo; de Mendoza, Carmen; Corral, Octavio
title: Main Differences Between the First and Second Waves of COVID-19 in Madrid, Spain
date: 2021-03-05
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2021.02.115
sha: 671c65762874d3b67bcb6798cf2955b600884bd6
doc_id: 720003
cord_uid: imm9ima9

BACKGROUND: The surge and rapid global spreading of SARS-CoV-2 infection has deeply challenged health services and disrupted social and economic activities worldwide. In Spain, the arrival of the first pandemic wave occurred in mid-March 2020 and lasted for 3 months, being abated with home confinement and strict lockdown. After relaxing measures during summer, a second wave began in mid-September and extended until Christmas 2020. METHODS: We compared the main features of SARS-CoV-2 infections during the two pandemic waves. We examined the information collected with rapid diagnostic tests and PCR at one university clinic in Madrid, epicenter of the pandemic in Spain. RESULTS: A total of 1569 individuals (968 during the 1(st) wave and 601 during the 2(nd) wave) were tested for SARS-CoV-2 specific antibodies using finger prick capillary blood. In addition, during the second wave, 346 persons were tested for SARS-CoV-2 specific antigens using either oral swab or saliva. The overall seroprevalence of first-time tested persons was 12.6% during the 1(st) wave and 7.7% during the 2(nd) wave (p < 0.01). Seroconversions and seroreversions were noticed within 6 months at low rates, both below 5%. Positive SARS-CoV-2 antigen during the 2(nd) wave was recognized in 3.5% of tested individuals, being two cases considered as reinfections. Severe clinical symptoms occurred in a greater proportion during the first wave compared to the second wave (27.8% vs 10.6%, respectively; p = 0.03). CONCLUSION: The cumulative seroprevalence of SARS-CoV-2 antibodies in Madrid at the end of year 2020 was around 20%. Seroreversions within six months occurred in 4%. Seroconversions and reinfections during the second wave were clinically less severe than during the 1(st) wave. Hypothetically, promotion of wider face masking, outdoor activities, and gathering restrictions during the 2nd wave most likely contributed to reduced exposures to large size inoculum.

The outbreak and global rapid spreading of SARS-CoV-2 infection from Wuhan, China, at the end of 2019 represent an unprecedented phenomenon in medicine. COVID-19 continues challenging health services and disrupting social and economic activities globally. In Spain, the arrival of the first wave began in mid-March 2020 and lasted with high numbers for 3 months. It was finally abated thanks to strict lockdown and home confinement. Following relaxing of measures during summer, a second wave began in mid-September and extended until Christmas 2020.

Although more than half of SARS-CoV-2 infections remain asymptomatic, individuals that experience symptoms range from influenza-like episodes (fever, cough, myalgia, etc.) to pneumonia and occasionally respiratory distress along with thromboembolic complications (severe COVID-19) (Griffin et al., 2021) .

Official records of total cumulative figures in Spain were of 262,814 confirmed SARS-CoV-2 infections during the first wave and 1,254,789 during the second wave (Ministerio de Sanidad, 2021) . Roughly, the impact on excess deaths during year 2020 was roughly of 80,000 in Spain, a country with a 47 million population (Instituto Nacional de Estadística, 2021) . This fatality rate for COVID-19 was one of the largest in Europe (Soriano et al., 2020a; Pastor-Barriuso et al., 2020) . Madrid, the country's capital and largest metropolitan region with a population of 6.6 million, was hardly hit and behaved as the national epicenter.

Herein we describe the main differences between the first and second waves of COVID-19 in Madrid, examining the clinical and diagnostic records of individuals attended at our university clinic.

The UNIR Medical Center is a university outclinic in downtown Madrid. Although it is mostly devoted to attention of university personnel and their relatives, medical care is also provided to other citizens when requested in advance.

All consecutive individuals attended during two trimesters of 2020 were retrospectively examined. The two periods covered the first and second waves of the COVID-19 pandemic, roughly from mid-March until the end of June, and from mid-September to Christmas.

We compared the main epidemiological and clinical features of SARS-CoV-2 positive persons and diagnostic testing procedures during the 3-month periods of the first and second pandemic waves, taking information collected with rapid tests and PCR confirmation. All individuals recruited in the study gave informed consent and filled a case report form J o u r n a l P r e -p r o o f specifically designed for this research. Recording included information on main demographics and clinical manifestations. The study was approved by the UNIR Ethics Committee.

In an attempt to simplify the recording and grading of clinical manifestations, we grouped the study population into two categories, those with absent or minor symptoms lasting three or less days versus those with mild or severe symptoms. The latest included fever, cough, headache, shortness of breath, anosmia, ageusia and/or malaise for at least 4 days.

SARS-CoV-2 specific antibodies were tested using finger prick capillary blood (PCL, Seoul, South Korea). SARS-CoV-2 specific antigen testing was performed only during the second wave. We used either oral swab (VivaCheck, Hangzhou, China) or saliva (PCL, Seoul, South Korea). All these serological tests have shown sensitivities and specificities above 90-95% examining distinct patient populations ( Thomson et al., 2021) . SARS-CoV-2 specific PCR testing was performed using a real-time commercial assay that targets S, N and ORF1ab genes on nasopharyngeal swabs. Positivity is reported when at least two genes are amplified with Ct values below 35.

All results are presented as absolute numbers and percentages, and as mean values and standard deviations. The comparison of rates was carried out using the Fisher exact test or the Chi-square test. Only p values below 0.05 were considered as significant. All calculations were performed using SPSS version 21 (SPSS Inc., Chicago, IL).

During year 2020, a total of 1569 individuals (968 during the 1 st wave and 601 during the 2 nd wave) were tested for SARS-CoV-2 specific antibodies using rapid tests. In addition, during the second wave, 346 persons were tested for SARS-CoV-2 specific antigens. All antigen positive individuals were confirmed by PCR.

The main demographics of the study population are recorded in Table 1 . Roughly 55% of tested individuals were female and their mean age was 42-years-old. Roughly 17% acknowledged having had positive household contacts. Nearly 40% were university personnel and their relatives, being the rest neighborhoods. The main reason for care visits were complaining of symptoms potentially associated with COVID-19 or suspicion of close contact with someone positive. Overall, there were no significant differences in the main demographics when comparing the two waves.

The overall seroprevalence of first-time tested persons was 12.6% during the first wave and 7.7% during the second wave. Seroconversions and seroreversions were noticed within 6 months at rates of 4.9% and 3.8%, respectively. Taking into account the rate of positives during the first wave and those positive for antibodies and antigen during the second wave, the estimated cumulative rate of infection by SARS-CoV-2 in Madrid was 20% by the end of 2020.

Positive SARS-CoV-2 antigen during the second wave was recognized in 3.5% of tested individuals, being all confirmed by PCR. Furthermore, all of them seroconverted for specific antibodies during follow-up. Two were considered as reinfections, being the interval J o u r n a l P r e -p r o o f between prior and recent episodes of 5 and 6 months, respectively. Interestingly, the first reinfection case was a 42-year old male with obesity that suffered pneumonia during the two episodes that required hospitalization. Unfortunately, we did not have the opportunity to perform sequence analyses to explore coronavirus genetic diversity.

The proportion of patients with clinical symptoms considered as mild or severe (lasting >4 days) compared to absent or minor symptoms (lasting <3 days) were significantly more frequent during the first wave compared to the second wave among antibody/antigen positive cases (27.8% vs 10.6%, respectively; p=0.03).

Spain was one of the European countries hardly hit by COVID-19 during year 2020. Official estimates were of nearly two million confirmed cases of SARS-CoV-2 infection and 80,000 deaths by the end of 2020 (Ministerio de Sanidad, 2021; Instituto Nacional de Estadística, 2021) . Madrid was the epicenter of the pandemic and experienced large surges of disease during the two major waves in spring and fall.

Given the shortage of diagnostic tests during the first surge of COVID-19, we conducted a pilot study in mid-May to unveil the proportion of individuals with asymptomatic infections and those with symptoms who could not be tested at the peak of the pandemic (Soriano et al., 2020b) . Testing capillary blood identified specific IgG in 93 out of 674 consecutive J o u r n a l P r e -p r o o f individuals (seroprevalence 13.8%). We noticed a significantly greater rate in family households and persons living in communities, with seroprevalence rates rising up to 19.2%.

A nationwide seroprevalence study performed during the same period of the first wave, known as ENE-COVID, examined specific IgG in more than 61,000 people across Spain (Pollán et al., 2020) . The overall seroprevalence rate was 5%, although several hotspot areas were identified, being Madrid one of them, with seroprevalence rates of 11.3%. The study highlighted that a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least one third of infections determined by serology had been asymptomatic. Clearly, underdiagnosis was common during the first wave of COVID-19 in Spain.

In our current study, the cumulative seroprevalence of SARS-CoV-2 antibodies in Madrid at the end of year 2020 was 20%. Seroconversions in people tested as negative during the first wave occurred in 4.9%. On the contrary, seroreversions in persons that had tested positive during the first wave were seen in 3.8% within six months.

Seroconversions during the second wave were clinically less severe than during the first wave. We hypothesize that large size inoculum leading to more severe SARS-CoV-2 infections (Guallar et al., 2020) during the first wave were more frequent than during the second wave. During the recent wave, wider face masking, promotion of outdoor activities, and gathering restrictions contributed to reduce coronavirus large exposures. In addition, other variables most likely contributed indirectly to ameliorate disease severity, including wider testing access (Soriano et al., 2020c) , allowing earlier identification and isolation; J o u r n a l P r e -p r o o f improvements in medical care, such as earlier use of corticosteroids and antibiotics; and average younger age of infected persons. The protective role of residual immunity in SARS-CoV-2 reinfections could not be assessed properly in our study given that only two patients had suspected reinfections (Babiker et al., 2021) . However, one of them suffered severe pneumonia in both instances.

In a serological survey performed by the Spanish government in December 2020, that included more than 51,000 individuals across the country, the seroconversion rate among those that previously tested negative for SARS-CoV-2 antibodies was 3.8% (Instituto de Salud Carlos III, 2021), slightly lower than the 4.9% rate seen in our study. In agreement with our findings, the Spanish nationwide study highlighted that the proportion of symptomatic patients was lower in the recent period compared to the first wave.

Our study has several limitations. First, individuals that experienced re-infections could not be examined in more detail. We did not perform phylogenetic analyses of viral genomes to confirm whether distinct strains were involved, including the new viral variants that seem to be more transmissible. Second, the determinants of the overall lower virulence of infected cases during the second wave compared to patients diagnosed during the first wave could not be explored deeper. The role of distinct medications used in each period could not be assessed properly, including corticoids, hydroxychloroquine, remdesivir, tocilizumbab, etc.

In summary, our study shows that by the end of year 2020 no more than 20% of the population in Madrid, a hotspot for COVID-19 in Spain, had been infected by SARS-CoV-2.

Thus, the benefit of prompt vaccination could be substantial, as current figures are far from J o u r n a l P r e -p r o o f reaching herd immunity. On the other hand, the clinical severity of recent SARS-CoV-2 infections has declined significantly, most likely reflecting the impact of social distancing and wider face masking on the average size of viral inoculum responsible for new infections.

Funding source: This work was funded in part by grants from UNIR COVID-19 projects TRAPES and SEVERITYGEN and the European Commission platform EASI-Genomics.

The study was approved by the UNIR Ethics Committee.

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 

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