High effectiveness of the SARS-CoV-2 vaccine in California, even with variants

Researchers in the United States and the United Kingdom conducted a study showing that the introduction of vaccines to protect against Coronavirus Disease 2019 (COVID-19) in the California population is proving effective.

The population-based surveillance study found that vaccination efforts prevent infection with the pathogen causing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in real-life conditions, despite the widespread distribution of worrying variants.

Commissioned by the California COVID-19 case-control study team, the researchers found that in fully vaccinated individuals (the second dose was received two weeks or more before), protection against SARS-CoV-2 infections was 86%.

Partial protection was also noticeable after a vaccine dose and within the first two weeks of receiving a second dose, according to teams at the University of California at Berkeley, the California Department of Health in Richmond, and the London School of Hygiene and Tropical Medicine.

“Our results show that the introduction of vaccines is preventing COVID-19 in the California population,” wrote Joseph Lewnard and colleagues.

However, the study also found that vaccine hesitation was an obstacle to achieving the levels of coverage required to achieve herd immunity.

The team says different approaches to communication and outreach will be required to remove these barriers to vaccine uptake in communities.

A pre-print version of the research paper is available on the medRxiv * server while the article is being peer-reviewed.

Effectiveness of the COVID-19 vaccine by doses received and time since last dose. Lines indicate 95% confidence intervals for estimates of vaccine effectiveness. The estimates were calculated using the conditional logistic regression.

Studies on the effectiveness of vaccines in practice are needed

The vaccines Pfizer-BioNtech BNT162b2 and Moderna mRNA1273 have been administered since December 2020 after their effectiveness was demonstrated in randomized controlled trials. By the end of April 2021, the vaccines had been given to 24% of California’s residents.

“Observational studies to characterize vaccine efficacy are needed to understand real-world performance and inform implementation programs,” said Lewnard and the team.

To date, most of the studies of vaccine effectiveness in practice have focused on healthcare workers and other frontline workers. They were also carried out in environments where worrisome variants were not yet a significant proportion of SARS-CoV-2 infections.

As of March 2021, however, the worrying variants B.1.1.7 and B.1.427 / B.1.429 occurring in the UK and California made up 69% of all SARS-CoV-2 isolates in California.

What did the researchers do?

To determine the effectiveness of the BNT162b2 and mRNA-1273 vaccines associated with significant prevalence of these variants, researchers conducted a case-control study of adult California residents with SARS-CoV-2 test results that were reported to the California Department of Health between February 24th and April 7th, 2021.

People who tested negative for SARS-CoV-2 infection (controls) were matched individually to SARS-CoV-2-positive people (cases) based on age, gender, geographic region and test week. A standardized questionnaire covering the demographics, symptoms and vaccination status of the participants was administered via telephone interviews.

Individuals were considered fully vaccinated two weeks after receiving a second dose of either vaccine.

To identify barriers to vaccine uptake that could affect future vaccination strategies, unvaccinated individuals were also asked about their willingness to receive a vaccine once they were eligible.

What did the study find out?

Of 325 cases, 23 (7%) and 13 (4%) reported receiving at least one dose of the BNT162b2 vaccine and the mRNA 1273 vaccine, respectively, and eight cases (2%) were considered fully vaccinated.

Of 260 controls, 49 (19%) and 49 (19%) reported receiving at least one dose of BNT162b2 and mRNA-1273, respectively, and 42 (16%) were considered fully vaccinated.

In the fully vaccinated subjects (at least two weeks since the second dose), the vaccine was 86% effective.

The effectiveness of the vaccine was 66% within the second week of receiving a first dose and 78% within the second week of receiving a second dose.

Rural-urban differences in willingness to vaccinate

Of 415 people who were not vaccinated, 39% of those living in rural areas and 23% of those living in urban areas said they were unlikely or unsafe to receive a vaccine once they were eligible. In contrast, vaccine reluctance did not vary significantly by age, gender, household income, or ethnicity.

The most commonly reported reasons for hesitation were safety concerns (24%) and side effects (26%).

“The introduction of vaccines prevents COVID-19 in real-world conditions.”

The researchers say the continued introduction of vaccines will prevent COVID-19 in real-world conditions in the general population.

In addition, partial protection was noted for two weeks after receiving the second dose, in line with previous estimates.

“It is important, however, that our results indicate considerable protection despite the widespread use of variants B.1.427 / B.1.429,” write Lewnard and colleagues.

Vaccine hesitation, however, is an obstacle to reaching the levels of coverage required for herd immunity. “Hence, different messaging and outreach strategies are needed to remove barriers to vaccine adoption in communities,” the team concludes.

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