COVID-19 vaccine boosters effective against Omicron in people with substance use disorder

COVID-19 vaccine boosters provide protection against Omicron infection and related hospitalization among people with substance use disorder, researchers from the University of Hong Kong have reported.

“Individuals with substance use disorder, including misuse of tobacco, alcohol [or] drugs, have higher risks of SARS-CoV-2 infection and severe outcomes vs those without,” wrote the researchers. Moreover, there are concerns that this population may have poorer response to COVID-19 vaccines than the general population due to their impaired immune systems. [Lancet Psychiatry 2023;doi:10.1016/S2215-0366(23)00111-6; Lancet Infect Dis 2022;22:1435-1443]

The researchers therefore conducted a matched case-control study (n=57,674) using electronic health databases in Hong Kong to evaluate vaccine effectiveness (VE) in patients with substance use disorder. “To our knowledge, this is the first study to evaluate VE in this population during the Omicron variant outbreak,” noted the researchers. Outcomes of the study were the risks of SARS-CoV-2 infection and COVID-19–related hospitalization. Cases and controls were matched by sex, age, index date and Charlson comorbidity index (CCI) for each outcome.

Substance use disorder patients with and without SARS-CoV-2 infection (n=9,523 and n=28,217, respectively) between 1 January and 31 May 2022 were chosen as cases and controls.

One dose of either BNT162b2 or CZ02 vaccine and two doses of CZ02 showed inadequate protection against SARS-CoV-2 infection among people with substance use disorder. In contrast, a significantly decreased infection risk was observed in those receiving two doses of BNT162b2 (VE, 20.7 percent; 95 percent confidence interval [CI], 14.0–27.0; p<0.0001).

Importantly, effective protection against SARS-CoV-2 infection was observed with three-dose vaccination, including three doses of BNT162b2 (VE, 41.5 percent; 95 percent CI, 34.4–47.8; p<0.0001), three doses of CZ02 (VE, 13.6 percent; 95 percent CI, 5.4–21.0; p=0.0015), and BNT162b2 booster after two doses of CZ02 (VE, 31.3 percent; 95 percent CI, 19.8–41.1; p<0.0001).

Moreover, 843 substances use disorder patients had COVID-19–related hospitalization (cases) between 16 February and 31 May 2022, while 40,485 matched patients were not hospitalized (controls).

Significant VE against COVID-19–related hospital admission was found after two-dose vaccination (both BNT162b2: VE, 73.3 percent; 95 percent CI, 64.3–80.0; p<0.0001) (both CZ02: VE, 59.9 percent; 95 percent CI, 50.2–67.7; p<0.0001) and three-dose vaccination (all BNT162b2: VE, 86.3 percent; 95 percent CI, 75.6–92.3; p<0.0001) (all CZ02: VE, 73.5 percent; 95 percent CI, 61.0–81.9; p<0.0001) (BNT162b2 booster after two doses of CZ02: VE, 83.7 percent; 95 percent CI, 64.6–92.5; p<0.0001).

“There was a clear dose-response relationship between the number of doses received and the magnitude of risk reduction of both SARS-CoV-2 infection and related hospital admission, [regardless of] vaccine types,” pointed out the researchers.

“Our findings highlighted the importance of the booster dose to reduce both SARS-CoV-2 infection and COVID-19–related hospitalization for people with substance use disorder,” wrote the researchers.

However, as of 31 May 2022, vaccine coverage of the first booster dose among people with substance use disorder was still lower than the general population (47.9 percent vs 54.5 percent). According to the researchers, policy changes are recommended to enhance access to booster vaccination in this vulnerable population.