Expert shares lessons from COVID-19

The world is out of the pandemic, but several subvariants of Omicron are still evolving, says Dr Adrian Chan, respiratory physician and intensivist at Mount Elizabeth Novena Hospital, Singapore, during his talk at APSR 2023.

“It started with Alpha, Beta, Gamma, and then Delta, which was probably the worst and the most disruptive of these variants,” recalled Chan, who was part of the organizing committee for APSR 2023. “Now, we have Omicron and its latest subvariants Eris and Fornax. COVID-19 has died down, but we are still facing new variants.”

Benefits of vaccination

COVID-19 vaccination campaigns have achieved their goals of protecting people against infections, reducing transmissions, severe disease, and even long COVID. In a meta-analysis, COVID-19 vaccines have been shown as highly effective against SARS-CoV-2-related diseases in real-world settings. [Int J Infect Dis 2022:114:252-260]

“At that time, Pfizer-BioNTech, Moderna, and CoronaVac were the prevalent vaccines. All three achieved vaccine effects to certain degrees,” said Chan. The efficacy of the Pfizer-BioNTech vaccine was 91.2 percent, the Moderna vaccine was 98.1 percent, whereas the CoronaVac vaccine was 65.7 percent. With this overwhelming benefit, local and global guidelines advocate for continued and widespread vaccination programmes.

 

mRNA vaccines at the centre stage

Out of the five COVID-19 vaccine types (mRNA vaccines, inactivated whole virus vaccines, viral vector vaccines, protein subunit vaccines, and bivalent vaccines), the mRNA vaccines took centre stage in the COVID campaign.

In spite that the majority of the population in Singapore had been vaccinated and infected, the country was not spared from the SARS-CoV-2 waves driven by Omicron sublineages BA.5 and XBB.

A Singapore study found that a previous infection during pre-Omicron conferred no or minimal protection against reinfection with Omicron BA.4, BA.5, and XBB whereas protection from a previous Omicron infection against XBB reinfection was lower and waned faster than protection against BA.4 or BA.5 reinfection. [Lancet Infect Dis 2023;799-805] This, according to Chan, highlights the importance of vaccination.

Keeping up to date with vaccination schedules is also equally important, he added. “Among individuals with a previous BA.1 or BA.2 infection, those who received a booster dose of an mRNA COVID-19 vaccine had greater protection against XBB reinfection than those who received only the primary vaccination series.”

Two or more vaccine doses given before COVID-19 infection also led to significant reductions in the rates of long Covid. [BMJ Med 2023;2:e000385]

Vulnerable populations

However,  there remains a substantial minority of immune-suppressed patients who would have low SARS-CoV-2 antibodies despite getting vaccinated, said Chan. In one study, for example, the rates of vaccine failure were particularly high in ANCA-associated vasculitis on rituximab, haemodialysis on immunosuppressive therapy, and solid organ transplant recipients. “Although T cell responses were generally maintained, these were also reduced in haemodialysis, allo-HSCT and liver transplant recipients. [Nature Medicine 2023; 29;1760-1774

“This group of patients, apart from getting vaccinated, are the ones we need to be careful about when they get COVID. Their COVID illness will likely be severe despite vaccination,” said Chan. “As lower serological or T cell responses were associated with hospitalization or death from COVID-19, identifying individuals who are most at risk remains imperative.”

As for the groups to prioritize for COVID vaccination, these include the elderly (age ≥65 years), healthcare personnel and essential workers, patients with high-risk medical conditions (cancer, CKD, COPD), with immunocompromised state from solid organ transplant, are obese (BMI ≥30), or with serious heart conditions, sickle cell disease, or T2D.

Vaccine safety

“The benefits of COVID-19 vaccination continue to outweigh any potential risks,” said Chan. “Some common side effects include fever, headache, and muscle aches. But what most people are concerned about is anaphylaxis or severe allergic reaction after COVID-19 vaccination. However, cases are rare.”

In fact, anaphylaxis only occurred at a rate of approximately 5 cases per one million doses administered. [Vaccine (Basel) 2023;11(2);432] Additionally, myocarditis is a recognised potential risk following mRNA vaccination, but the incidence of myocarditis remained rare in Singapore.

Currently, the US Centers for Disease Control and Prevention recommends that everyone ages 6 months and older get vaccinated to protect against COVID-19 and its potentially severe complications.

“COVID-19 vaccination works,” Chan emphasized. “Still, there are unanswered questions. We need to improve vaccine literacy among patients. We need updated COVID-19 vaccines … one like the influenza vaccine that can predict the upcoming stream.”